A Level Biology Revision Notes

Comprehensive A Level Biology revision notes providing information and assistance for all UK examination boards (AQA, OCR, Edexcel) as well as international curriculum (CIE).

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Actin

Introduction When it comes to muscle, understanding its structural organization is necessary to understand physiology. If there‚Äôs altered physiology, then it will be termed as Pathology. The sarcomere is highly organized, containing long cylindrical filaments called myofibrils that run parallel to the axis of the fiber. The dark bands on myofibrils are called A bands …

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Tropomyosin – A Muscle Protein

Introduction When it comes to the molecular mechanism of muscle contraction we are up with the explanation of Sliding Filament Theory. A sarcomere, which serves to be the basic unit of muscle contraction is made up of myofibrils which in turn are composed of actin and myosin filaments. The ratio of actin to myosin filament …

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Muscle and Contraction

Introduction Animals have a lot of differences from the plants in their mode of living, ways of obtaining food, adaptations to their habitat, etc. One of the major differences between animals and plants is that of movement or locomotion. Animals can move from one place to another while plants spend their life at the same …

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Myofibrils

Introduction Skeletal muscles are the most abundant tissues found in animals. They make up more than 40% of the total weight of an average human. These muscles are responsible for all kinds of movements exhibited by a human being. They are under voluntary control meaning that we can consciously control their contractions. Skeletal muscles are …

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Myosin

Introduction The contraction of skeletal muscles is responsible for all kinds of movements exhibited by animals. This contraction is possible due to the contractile proteins present inside the skeletal muscle cells. The contractile proteins, along with the regulatory proteins are organized in the form of myofibrils. Myofibrils are further divided into sarcomeres that serve as …

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Synaptic Transmission

Introduction Humans and other vertebrates have developed a highly efficient system of communication, the nervous system. It is a network of interconnected neurons that are capable of generating and transmitting nerve impulses. The communication process is based on the successful transmission of nerve impulses from one neuron to the other. Neurons are connected via specialized …

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Neural Summation

Introduction The nervous system is specialized to carry nerve impulses from one organ of the body to another. Nerve impulses are carried by neurons. The action potential is generated in a neuron when it is excited by some stimuli or by the nerve impulse coming from the surrounding neurons via synapses. In most of the …

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Taxis and Kinesis

Different types of movements can be seen in unicellular as well as multicellular organisms. The motives of these movements are also different. An organism may exhibit movement to find food, to seek shelter from heat or cold, to save itself from a predator, to find water supplies, or to search for prey, etc.  Sometimes,  movements …

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Autonomic Nervous System (ANS)

Introduction All the functions (processes) of the human body are either voluntary or involuntary. Functions like sight, movement, speech, etc. are some of the few voluntary actions. And many functions vital for the human body like breathing, heart rate, sweating, etc are involuntary. All these conscious or otherwise functions are controlled by the nervous system. …

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The Reflex Arc

Introduction Our body performs many actions that are not under conscious control. The nervous system of our body detects certain stimuli and performs a response action before we become aware of the stimulus. Reflex action is one example of such responses. A reflex action is an involuntary response to a stimulus, mostly a pain stimulus, …

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